(1) Field of the Invention
The present invention relates to a high quality and high resolution digital zooming system and method. More particularly, this invention relates to a high resolution digital zooming system and method which enhances the resolution of a camera image by extracting and using dynamic image information from across a plurality of image sequences.
(2) Description of the Related Art
Techniques for magnifying images have been developed using image processing techniques. When magnifying an image, the number of pixels for displaying the image increases; accordingly, image magnification is closely related with resolution enhancement.
Generally, methods to form high resolution magnified images from small-sized low resolution images employ an interpolation algorithm which only uses information from spatially adjacent pixels in a static image. However, because the quantity of image information remains constant, such methods can increase the size of the image, but can not substantially enhance its resolution. One such method was described in the U.S. Pat. No. 5,307,167, issued Mar. 16, 1992, and entitled "Digital Zooming System Utilizing Image Buffers and Employing an Approximated Bilinear Interpolation Method" (Inventors: Sung-Wook Park and Joon-Ki Paik, Assignee: Samsung Electronics Co., Ltd.).
A conventional zoom system will now be described with reference to FIGS. 1 through 4.
As shown in FIG. 1, an image is sampled by a regular sampling interval (namely, a distance between pixels) about an input image. In the drawings, two-dimensional image signals are regarded as one-dimensional image signals in order to more simply facilitate an understanding of image magnification theory. Herein, subpixel image information (information between pixels in the image corresponding to a magnified zoom image centered about a target within the image) is not obtained, so the amount of obtainable image resolution corresponds to the sampling frequency used. The subpixel information needed for image magnification is instead determined by interpolating from the known image information of adjacent pixels.
FIG. 2 shows an example of a conventional zoom method using interpolation. In this example, subpixel information P'(x') (where x'=0, 1, . . . N, N-1) needed to magnify an image by two times is estimated by first order interpolation. The subpixel information can be expressed by the following equation. EQU P'(x')=(m-k).multidot.P(x)+k.multidot.P(x+1), (x=0, 1, . . . , N-1)
where k (0&lt;k.ltoreq.1) is an interpolation coefficient. In FIG. 2, the value of k is 0.5.
By applying the above method to both the horizontal and vertical components of the image, a spatially interpolated image can be obtained. Although various image processing methods have been adopted to preserve the higher frequency image components (e.g., second order interpolation, interpolation by frequency analysis, and inverse filters), the image resolution obtainable using interpolation is still limited by the sampling frequency.
FIG. 3 shows an example of a conventional digital zoom system used in a video camera. In the operation of this system, an image input through a lens is converted to an electrical signal by a charge coupled device ("CCD") 31, and is then converted to a digital signal by an analog-to-digital converter ("ADC") 32. A digital zoom 33 spatially magnifies the image signal using first order interpolation. Finally, a digital-to-analog converter ("DAC") 34 outputs a resultant image signal.
FIG. 4 shows another example of a conventional digital zoom system used in a video camera. This zoom system compensates for image shaking, such as that caused by hand motions in a hand-held camera, by detecting the pixel motion of an image, and then performing a digital zoom function about the compensated image.
In the operation of the system of FIG. 4, an image input through a lens is converted to an electrical image signal by a CCD 41. The electrical image signal is converted to a digital signal by an ADC 42. A motion detector 43 detects pixel motion from the input image signal. A digital image stabilizer 44 stabilizes the input image signal. A digital zoom 45 spatially magnifies the input image signal using first order interpolation. Finally, a DAC 46 outputs a resultant image signal.
In conventional digital zooming systems, the method used to spatially magnify image data is responsive only to a partial area of the input image. Therefore, spatial resolution is inversely proportional to a scale factor of a screen. This degrades image quality and limits magnification.